This invention relates to feeders for web material for use with printing and more particularly die-cutting apparatus of the kind which comprises a pair of rolls of which one (called the impression roll) carries a web-treatment area in the form of, for example, a stereo or forme. When the forme, for example, extends over the whole of the periphery of the impression roll the web may be fed continuously through the nip between the rolls at the same speed as the peripheries of the rolls and a series of printed and/or cut blanks produced along the length of the web, and the small amount of waste between successive blanks formed in or from the web will be equal in length to the space between the leading and trailing edges of the forme or the like measured about the periphery of the roll.
Apparatus of this kind is required to produce blanks varying in size from small to large, and the largest which may be produced is equal to, or very slightly less than, the dimension of the periphery of the roll. With all smaller blanks, the length of web between each two blanks is waste and the amount of waste which is produced may be unacceptable. For this reason it has been the more usual practive hitherto to produce such blanks from discrete pieces of material i.e. to cut the web into blanks and feed the same individually through the apparatus, instead of feeding the web material through the apparatus, thus introducing an additional machine and an extra handling step.
It is also known, for example from British Pat. No. 1 324 169 to provide a web-treatment apparatus comprising a continuously-rotatable rotary member having a part-circumferentially extending web treatment area, a first counter pressure member co-operable with said web treatment area to effect feed of the web therebetween during a part of each revolution of the rotary member, a drive element and a second counter pressure member associated therewith, and variable drive transmission means comprising cam means rotatably fast with said rotary member and a cam follower co-operable with the cam profile of said cam means to transmit rotational drive to said drive element in such a way that, during each revolution of the rotary member, said drive element is accelerated in the same rotational sense as the rotary member immediately prior to feed of the web by said rotary member and the first counter pressure member, is decelerated in said same rotational sense immediately subsequent to termination of feed of the web by the rotary member and the first counter pressure member to arrest feed movement of the web, and is accelerated and then decelerated in the opposite rotational sense during the remainder of each revolution of said rotary member to effect reverse feed of the web, the second counter pressure member being co-operable with said drive element during such acceleration and deceleration of the latter to impart feed movement to the web and said cam means comprising a pair of cam parts which are adjustable relative to one another to vary the cam profile. Such apparatus, as described in the above British patent 1 324 169 has the advantage of enabling a series of successive treated areas to be provided along the length of the web material without waste between each two successive areas, but inevitably, the maximum length (measured along the web) of each discrete treated area is less than the periphery dimension of the treatment roll. Typically for example 112.degree. of the angular movement of the treatment roll has been required for the minimum cycle of operation involving the acceleration and deceleration steps referred to. Effectively this has meant that the maximum length of blank which could be provided by such apparatus is equal to the arcuate length of the treatment roll over the remainder, i.e. some 250.degree. of its periphery.